The present invention claims priority based on Japanese Patent Application Serial No. H10-260932, the contents of which are incorporated hereinto by reference in its entirety.
1. Field of the Invention
This invention relates to a method for producing glass substrates of high-quality crystalline glass or sheet glass, which are for magnetic disks of a high-capacity type and which have good adhesiveness and good impact resistance with no pit.
2. Description of the Related Art
Many magnetic disk substrates produced through bed nickel/phosphorus plating on the surface of an aluminium alloy blank have been used for magnetic recording media for computers. Glass substrates have come to be used for small-sized notebook-type or mobile personal computers. Unlike in the case of aluminium substrates, a magnetic film can be directly applied to glass substrates with no bed plating. However, for realizing glass substrates for magnetic disks with higher memory capacity, studies have been made on a method in which like aluminium substrates, glass substrates are previously plated with nickel/phosphorus and then coated with a magnetic film thereover. Thus using glass substrates in place of aluminium substrates reduces head snapping, as glass substrates are hardly dented against the pressure of heads thereto as compared with aluminium substrates.
As a rule, an ordinary method of electroless plating on non-metallic substrates or oxide or plastic substrates comprises pre-treatment of, for example, adsorbing Sn onto their surface followed by forming a film of a catalytically-active metal (e.g., Pd, Pt or Au) with low hydrogen overvoltage over the Sn coat, as in Japanese Patent Laid-Open Nos. 19932/1978 and 85614/1973. More concretely, the pre-treatment for plating includes, for example, degreasing, etching, sensitization, activation and sensitivity-enhancing treatment. The thus-pretreated surface is then plated with nickel/phosphorus.
The plated substrates are polished with known abrasive grains of, for example, alumina to be those for magnetic disks. The polished substrates are then coated with a magnetic film through sputtering on their mirror-finished surface to be magnetic recording media.
The sensitization pre-treatment for nickel/phosphorus plating on glass substrates is often problematic in that, if the substrates receive too much tin on their surface in the pre-treatment step, the excessive tin will drop off from the surface to be caught by the plating film. As the case may be, the water-soluble oil used for lapping the substrates in the pre-treatment step will remain in the hollows of the lapped substrates. In that case, the substrates shall have pits in their surface.
Given that situation, the object of this invention is to solve the problems noted above that have heretofore been inevitable in producing plated glass substrates for magnetic disks for which are used various types of glass, such as crystalline glass or sheet glass with high hardness, in place of aluminium. Specifically, the invention is to provide a method for producing glass substrates for magnetic disks which have good impact resistance even for mobile applications and are therefore suitable to small-sized or mobile computers. When used in recent notebook-sized or mobile computers where the head is located as closely as possible to the disk substrate therein, the substrates produced in the invention are not scratched by head snapping around them.
The method for producing magnetic disk substrates of the invention comprises pre-treating glass substrates for at least degreasing, etching, sensitization with tin chloride, activation and sensitivity-enhancing treatment in that order followed by forming a nickel/phosphorus film on their surface and polishing them, and is characterized in that, after the sensitization step but before the activation step, the substrates being processed are washed in hot pure water at a temperature of not lower than 50xc2x0 C. for a period of from 20 to 90 seconds, and after the sensitization step but before the step of forming a nickel/phosphorus film on their surface, the substrates are heated at a temperature of not lower than 70xc2x0 C. for a period of from 5 to 100 minutes. The method of the invention solves the problems noted above.